The present invention relates to polybutylene (polybutene-1) polymer blend and a film made from such blend. More particularly, the invention relates to a polybutylene polymer blend having a unique molecular weight distribution and a film having a unique combination of good hot tack, low heat sealing temperature and high clarity. Even more particularly, the invention relates to a polybutylene blend made by chemical degradation (also known as chemical cracking or random scission by chemical means) of a portion of a reactor polybutylene and blending back the cracked portion with the original parent reactor polybutylene. The resulting blends have been shown to possess a unique molecular weight distribution not achievable in either the pure uncracked or cracked polymers, such unique molecular weight distribution manifesting itself in unusual combinations of processing behavior and physical properties of film fabricated from the blend.
Polybutylene film, as known commercially, shows deficiencies in hot tack and processing behavior, as well as clarity. Heretofore, it was thought that the cause of this unfavorable balance of properties was inherent in the polybutylene itself. However, applicants have found that a unique molecular weight distribution of the polybutylene polymer blend and resulting film surprisingly improves the hot tack, lowers the heat sealing temperature and improves the clarity of the composition and film.
Hot tack may be defined as the bonding strength between two pieces of polymer film at the point immediately after their having been joined together by application of heat and while the polymer is in a semi-molten solidifying state. Films are often made into packages which are sealed by applying heat to contacting surfaces. The seal must attain sufficient strength to contain the materials within the package. Not only does the weight of the material or product contribute to a tendency for seals to release, but in addition, the pressure of air used to assist in transport of the product may exert additional pressure against the seal.
In addition to good hot tack, a low heat seal initiation temperature is desired so that a film may be sealed at a relatively low temperature. Commonly used seal layers, such as propylene-ethylene copolymer, melt at a high temperature relative to the main packaging film, i.e. it has a high heat sealing temperature.
In addition, it is important that the film and ultimate package possess high clarity for good "see-through" properties to gain commercial acceptance. Heretofore, polybutylene films for packaging have been deficient in one or more of these desired properties.
Japanese Pat. No. J-53034834 discloses a transparent strong adhesive tape attained by tackifying one surface of biaxially drawn films comprising polymer mixtures containing 20 to 80% by weight of polypropylene and 80 to 20% by weight of polybutylene having a molecular weight of 500 to 20,000, which gives good transparency to the film.
U.S. Pat. No. 3,198,779 discloses a process for producing a synthetic hydrocarbon resin which comprises thermally cracking a polybutene-1 resin with molecular weight of at least 50,000 and an isotactic content of at least 10% by weight by introducing the polybutene-1 resin into a thermocracking zone at a temperature from 250.degree. to 450.degree. C. under a pressure of from 0.001 to 25 mm of mercury and under non-oxidizing conditions and maintaining the polybutene-1 resin in the zone until the molecular weight of the resulting hydrocarbon is within the range of 3,000 to 45,000 and recovering the resin from this cracking zone. This invention relates to the recovery of hydrocarbon resins useful as wax substitutes. These resins have low molecular weights and the advantage of good solubility in hydrocarbon solvents. These resins are used in the production of coatings resulting in superior flexible coatings which will not crack upon flexure of the substrate to which the coating is applied.